A release film is used as the process film for producing films by casting of resins such as polyurethane resins, polyacrylic resins and polyvinyl chloride resins, the process film for molding of green sheets for laminated ceramic condensers and the protective film for pressure sensitive adhesives in pressure sensitive adhesive products.
In the release film, in general, a layer composed of a releasing agent such as a silicone-based resin and a non-silicone-based resin, which is, for example, a compound having a long chain alkyl group or an olefin-based resin, is formed on the surface of a substrate film. When a release film obtained as described above is peeled off after being used for the above application, an undesirable phenomenon arises in that static electricity is formed at the time of peeling, and foreign substances are attached to the product.
To prevent the undesirable phenomenon, it is conducted that the release film is subjected to an antistatic treatment.
For the antistatic treatment of a release film, in general, ionic compounds such as quaternary ammonium chloride have been used frequently. However, when the ionic compound is used for an antistatic layer, the antistatic property is greatly affected by the humidity of the atmosphere. When the ionic compound is contained in a releasing agent layer which uses silicone resin of the addition reaction type, there is the possibility that curing of the resin is adversely affected.
A system in which an electrically conductive metal-based filler such as a metal or a metal oxide is dispersed into a resin is proposed (for example, refer to Patent Reference 1). In this case, the particle diameter is great, and there is the possibility that smoothness of the film is adversely affected. Moreover, the antistatic property is unstable since uniform dispersion of the metal-based filler in the resin is difficult. A great amount of the filler must be added to exhibit the stable antistatic property, and the cost is inevitably increased. When the antistatic property is stabilized by increasing the amount of coating, there is the possibility that blocking takes place due to the increase in the thickness of the resin layer.
To overcome the above problems, a release film having the antistatic property in which, for example, an antistatic layer obtained by photo-curing a coating material of the photo-curing type composed of an electrically conductive macromolecule, a photo-initiator and a binder is formed on the surface of a substrate film, and a releasing layer composed of a silicone resin of the addition type is formed on the antistatic layer, is disclosed (for example, refer to Patent Reference 2).
The above release film is a film suppressing adverse effects on the curing and exhibiting the excellent releasing function and antistatic function by forming a releasing layer composed of a silicone resin of the addition type on the surface of the antistatic layer containing the electrically conductive macromolecule. However, the release film is not always satisfactory with respect to the productivity since the operations of forming the antistatic layer on the surface of the substrate film and forming the releasing layer on the formed antistatic layer are necessary.
[Patent Reference 1] Japanese Patent Application Laid-Open No. 2002-179954.
[Patent Reference 2] Japanese Patent Application Laid-Open No. 2005-153250.